Propulsion screw



June 18, 1929. vr. TlsMl-:R

PROPULSION SCREW Filed Feb. 27, 1928 mehr Effe fuk/' 73's mer fa@ 1p 7 flown-ey Patented .lime 1s, 1929.

UNITED STATESy PATENT OFFICE.

FRIEDRICH TISMER, OF BERLIN, GERMANY.

PROPULSION SCREW.

Application filed February 27, 1928, Serial No. 257,473, and in Great Britain February 3, 1928.

This invention relates in general to propellers and screws of the kind employed on air and water craft and is concerned more" particularly with propeller-s and screws of the 5 type provided with so-called nozzle o1` slot devices, that is, screws the blades of which are provided with nozzle-like orifices or passages or with nozzle-like slots or grooves at the trailing edges or are furnished with both these devices.

According to the present invention, the object of which is to improve the properties of screws of this type, provision is made of a. plurality of grooves or slots running through or over the trailing edges of the blades from the higher pressure side to the lower pressure side of the blades and tapering or narrowing down in cross-section from said higher pressure to said lower pressure side, or of completely enclosed passages or orifices tapering similarly to the grooves but located in a position forwardly of the trailing edges. If necessary both devices may be employed together on the same screw. These devices exercise nozzle like effects on the air or other medium and facilitate the pressure compensation or equilization at the trailing edges of the screw. v

Screws with slots at the trailing edges of the blades are already known but in these known screws the slots flare outwardly from the forward edges to the rearward edges of the blades. Furthermore air screws are known wherein the blades are interrupted, the interruptions being either very wide and thus allowing the passage of a considerable amount of air or flared outwardly from the higher pressure side to the lower pressure side. F inally supporting surfaces for air craft are also known which have longitudinal slots at the leading wing edge whereby the profile of the surface is subdivided into a number of separate profiles disposed one behind the other in a louvre-like arrangement.

By way of example the ap lication'of the invention to an air craft prope ler or air-screw.

is illustrated diagrammatically in the accompanying drawing in which:

Fig. 1 is a cross-section of the air-screw on the line A-B of Fig. 2, and

Fig. 2 shows a elevation.

In the drawing the reference letter a indicates the air-screw blade, b the high pressure side thereof, c the lower pressure side, l the 55 openings on the high pressure side and e the openings on the lower pressure side of passages z' tapering according to the invention, f the portion on the high pressure side of similarly tapering grooves, g the portion on the low pressure side thereof and L the trailing edge of the air-screw blade.

The bores ,or passages and the slots or grooves which taper from the high pressure side to the low pressure side of the blade may be given a twist or made helical to conform part of the air-screw in side -with the air or other flow and their crosssections may be of various shapes. The crosssection of the bores or passages may be round, oval or oblong and that of the grooves rectangular, triangular, trough-shaped or the like. The screw may be constructed with grooved or slotted metal members mounted on the trailing edges of the blades and the bores` may'be lined if necessary.

Provision may also be made for opening and closing or eonstricting the bores and grooves, this may be effected automatically, for example with the aid of centrifugal force, or arbitrarily by manual or mechanical operation.

What I claim is:-

1. In a propulsion screw the combination with a blade for the purpose of facilitating pressure equilization between the two sides of the trailing edge of said blade of passages y associated with said trailing edge and tapering from the higher pressure side to the lower pressure side thereof, said passages being angularly arranged relative to the width of 90 the blade.

2. In combination with the blades of a propulsion screw, surface passages formed across thel trailing edges of said blades and tapering from the higher pressure side to the lower pressure lside thereof, said passages being angularly arranged relative to the width of the blade.

3. In combination with the blades of a propulsion screw, nozzle-like passages tapering from the higher pressure side to the lower pressure side of the blades and formed in the trailing edges of said blades, said passages being angularly arranged relative to the width 5l of the blade. v

4. In a repulsion screw, t-he combination with a bluse of two series of passages tapering from the higher pressure side to the lower pressure side thereof, one series being formed across the trailing edge of said blade and the 10 other through the blade in proximity to said edge, said passages being anoularly arranged relative to the width of the blade.

In testimony whereof I hereunto aix my signature this 13 da of February, 1928.

FR EDRICH TISMER. 

